Electronic switching system



March l5, 1949. v J. E. sM'lTH x-:TAL

ELECTRONIC swITcl-IING SYSTEM Filed Sept. 16, 1943 3 Sheets-Sheet l /6 I '/0 2 a? i f4 ,sw/Td/ff i /A//JUT March 1 5, 1949. 1 E, sMlTH Er AL 2,464,353

ELECTRONIC SWITCHIG SYSTEM Filed Sept. 16 1943 3 Sheets-Sheet 2 AAAAAAAA vvvvvvvv INVENTo :I Erna t Zugang/E. ghe/2l( ml 191 I Bwg A T'Toe/VEK ALIA March l5, 1949. J, E sMlTH lET AL 2,464,353

ELECTRONIC swITcHING SYSTEM Filed Sept. 16, 1943 5 Sheets-Sheet 3 MALLA AAAAAAA AAAAAAAM' vvvvvvr vvvvvvv" A TTG/@NEX Patented Mar. l5, 1949 UNITED STATES FAT NT OFFICE ELECTRNIC SWITCHING SYSTEM of Delaware Application September 16, 1943, Serial No. 502,616

(Cl. Z50-27) Claims.

The present invention relates to electronic switching means and more particularly to an electronic switching system in which the controlling wave or controlling impulse does not appear in the output of the system.

Electronic switching devices in the prior art have passed the control or switching signal as well as the signal or impulse which is to be interrupted, as in some switching systems, or selectively passed to diierent channels as in other switching systems. In these prior art switches and switching systems, if the switching signal were not passed, then a large transient voltage or current pulse followed each switching operation. Where neither of the above disadvantages are present, the signal band width of the circuits involved in the switching operation was restricted by a transformer. The switching means of the invention to be disclosed suffers from none of the foregoing disadvantages.

The primary object of the present invention is to provide in a novel manner for the suppression of the control wave, impulse, or switching signal in an electronic switching system.

Another object of the invention is to provide novel means for the control of amplifiers employed as electronic switches.

A further object is to provide a novel method of selectively associating any one of a plurality of input circuits with any one of a plurality of output circuits.

Still another object is to provide a novel arrangement for supplying anode Voltage to an electronic repeater in accordance with a control impulse or signal.

Still further objects of the present invention will become apparent and suggest themselves to those skilled in the art upon reading the following specication in connection with the accompanying drawings in which:

Fig. 1 is a diagrammatic showing of an electronic switching system in accordance with the invention;

Fig. 2 shows an arrangement similar to Fig. 1 but in slightly modied form;

Fig. 3 shows still another modification of the invention as embodied in an electronic switching system; and

Fig. 4 is a schematic showing of a. power supply source of usual form which may be used in conjunction with Fig. 3 of the drawings.

The switching system of Fig. 1 of the drawings in normal operation is capable of alternately switching signals from two input circuits to a single output circuit. The input terminal of one 2 of the switching circuits is indicated at l and is connected by way of the usual blocking condenser l2 to the grid lli of a space discharge tube i6 connected as a phase inverter. It will be understood that the remaining terminal of the electronic switch is provided by the ground connection Il when the system is connected to apparatus which is grounded in the usual manner. However, the connection Il may be part of the chassis of the equipment, a connection to earth, or a terminal on the usual power supply equipment.

The space discharge tube l@ serves as a phase inverter to feed a pair of discharge tubes I9 and 2D which are connected in push-pull relationship. The grids 22 and 23 respectively of these tubes are connected through blocking condensers to the `anode and cathode of the phase inverter tube IB. The cathodes of the discharge tubes i9 and 20 are connectd through a cathode resistor 24 to a source of positive potential connected to a terminal 23. Grid resistors 28 and 29 are provided for the grids of the discharge tubes i9 and 20.

The second input connection for another series of signals is provided by a terminal 3l which is connected by way of a blocking condenser 32 to the grid 34 of a discharge tube 36 which is connected in the same manner as the discharge tube I6 to serve as a phase inverter.

Discharge tubes 38 and 39 serve as a pushpull amplier in the path of signals from the terminal 3| in the same manner that discharge tubes I9 and 20 serve as a push-pull amplifier in the path of signals from the input terminal l0. The cathode resistor 4I for the cathodes of the discharge tubes 38 and 39 is connected through a terminal 42 to a suitable source oi positive potential. The terminals 26 and l2 may be connected to the same source if desired.

A pair of Thyratron or other gas discharge tubes M and e5, connected in the well-known back-to-back circuit, is shown by way of example to supply switching voltage to the push-pull stage comprising discharge tubes i9 and 2li and also the push-pull stage comprising discharge tubes 38 and 39 in accordance with a controlling wave or controlling impulse. While the back-toback gas discharge tube circuit is shown as the means for supplying the switching voltage, the switching voltage may be obtained from any source such as relays or high vacuum tubes for example. A trigger circuit having only one stable position or other similar circuit could be used to supply the switching voltage to the switch 3 comprising the tubes and 2i] or the switch comprising the tubes 38 and Sii. With such a device, either or both switches could be switched and then automatically returned after a predetermined interval of time.

The controlling signal is applied to the grids il and i8 of the tubes lll and d5 at input terminals i9 and 5l. Terminal 52 serves as a common ground when the input signal is applied from a push-pull stage. The push-pull input connection provided by trie terminals iii to is suggestive only of a means for supplying a switching control signal, and it will be understood by those skilled in the art that a single-ended input may be used Witn the tubes fill and t connected 'together in a self-restoring trigger circuit.

The plate voltage oi' the gas tube dal serves as the plate supply voltage for the tubes i9 and 2li. Similarly, tne plate voltage of the gas tube l serves as a plate supply voltage for the tubes Sii and 39.

It is wel known that if a pair of gas tubes is connected as shown for the tubes lil and lib, then only one of the tubes can be conducting at a time. Igniting the other tube automatically extinguishes the one previously conducting. Therei'ore, depending on whether ill is conducting or non-conducting, the plate supply voltage for the tubes iii and 2S is substantially equal to the voltage drop in the tube lill, or it will be the voltage of the plate supply source connected at 55. The positive voltage, which is connected to terminal 2%, should be approximately equal to or greater than the drop across the tube lli when it is conducting. With this arrangement the plate to cathode voltage of the tubes lli and 2b will vary between a negative value or zero and a positive value sufficiently high for normal operation. Therefore, when the tube fill is conducting, the tubes i9 and 2li will be non-conducting so that the signal applied to the terminal lil will not be transmitted by the tubes i9 and 2li. Tube i5 will be non-conducting so that normal plate voltage is supplied to the tubes 38 and 3.9, and the signal applied to the terminal 3l will be transmitted by these tubes.

The signal transmitted by the tubes 38 and 39 in this manner will be supplied to a tube 5S. The input electrode (il of a tube b2 is connected to the output circuit of the tubes lil and and this tube t2 corresponds in function to the tube 59. The anodes Eli and 65 of the tubes 59 and 62 respectively are connected to an output load resistor 68. The terminal 5B of the load resistor is connected in the usual manner to a source of positive anode voltage.

If the gas tube l5 is ignited, the signal from the terminal 3l will be blocked, and the signal from the terminal lil will be transmitted by the tubes I9 and 2b and the tube il? so that it appears across the load resistor 68. In this manner signals from the terminals lil and 3i appear alternately across the load resistor 68.

The tubes 59 and $2 are connected in such a manner that a push-pull signal input will be amplied, but a push-push signal input will not be present across the output load resistor d3. These tubes, therefore, act the same as a transformer for going from a push-pull input connection to a single-ended output connection. The action of tubes connected in this manner is described in detail in the application of C. N. Gillespie for Discharge tube circuits, Serial No. 500,618, led August 31, 1943. The tubes 59 and 62 are shown as having their input circuits'conductively coupled to the output circuit of the preceding tubes. This conductive connection may also be employed where only a single preceding tube is used.

Considering the tube S2 and its connections, the same value of positive D. C. voltage will be coupled into the grid circuit as into the cathode circuit of the tube. As a result, the net gridcathode voltage from this source will -be Zero. This is true because the D. C. voltage is supplied as a push-push voltage. Since the switching voltage, that is, the voltage applied through the agency of the gas discharge tube trl, is also push-push, it will not be present in the output. The desired signal, being applied push-pull to the tub-e 52, will be present in the output circuit oi this tube.

An adjustable `resistor 'iii in the grid circuit of the tube b2 is provided for the purpose oi balancing out the switching voltage resulting from signals applied to the terminal lil. A resistor il is connected in both the grid and the plate circuits of the tube 52. Therefore, the values oi' the resistors lil and 'il will not necessarily be equal for cancellation of push-push voltages.

The switching transient in the output of the tubes 59 and G2, or either, has been found in practice to be very small. Ii there is any switching transient at all, it is due to the difference in the total capacitances and inductances in the two sides oi the push-pull system feeding the tube 59 or the tube t2 and the capacitances and inductances in the tubes themselves. These effects can be overcome by properly neutralizingA the unb-alance in the inductances and capacitances. While triodes have been chosen to simpliiy the disclosure and description of the embodiment of the invention shown in Fig. 1 of the drawings and the other figures, other types of tubes such as tetrodes and pentodes are equally applicabe and, in some cases, preferable.

It should be noted that the switching arrangement comprising the tubes i9, 2B, and 62, due to its direct coupled connection, is capable of passing all frequencies down to and including direct current. input applied to the terminal i3, direct current coupling may be employed from the terminal I0 to the input connections to the tubes i9 and 2U. The foregoing is also true of the switch comprising the tubes 33, 35i, and 59,

A transformer cuold be used in the plate circuits of the tubes, lil and 20, or the tubes 38 4and eliminating the need for the tube G2 or the tube 59 and their associated circuits. If switching transients are to be avoided, the windings of the transformer, if it is used, must be carefully balanced.

The phase inverter tube i6 could be omitted and the input signal could be fed single ended to either the tube I9 or the tube 2i?. In either case the output from the tube b2 wouldbe reduced to approximately one-half of its former value. Assume a where the signal is fed only to the tube i il. A signal will exist in the grid circuit of the tube due to the plate current of the tube i9 in the cathode resistor 24. In this case the cathode resistor may be bypassed or left unbypassed if desired.

Fig. 2 of the drawings discloses-an arrangement very similar to the arrangement disclosed in Fig. 1. The arrangement of Fig. 2 is used for switching a common input `signal between two-output circuits. Discharge tubes 1B and Tl, correspond- 1f it is desired to switch a direct current.

5. ing in function to the tubes 59 and 62 of Fig. 1, have separate output connections 18 and 19. Separate load resistors 8| and S2 are provided with the terminals 83 and 84 thereof connected to a suitable source of positive potential.

Gas discharge tubes 86 and 81 correspond in function to the tubes 43 and 44 of Fig. 1. The controlling signal or controlling impulses are applied at the terminals 89 and 9|, the terminal 92 being provided for convenience as a common ground connection.

Discharge tube 93 serves the same purpose as either the tube |6 or 36 in Fig. 1 of the drawings and is connected through coupling condensers 94 and 96 to the grids 98 and 99 of the discharge tubes |0| and |02 respectively. The tubes|6| and and |02 are controlled by a gas discharge tube 86.

The grids |63 and |64 of a pair of tubes |86 and |61 are also connected to the coupling condensers 94 and 96 so that these elements are effectively in parallel and the two pairs of tubes have common grid resistors |68 and |99 and a common cathode resistor The tubes |66 and |81 are controlled from the gas discharge tube 89 in a manner similar to the control of tubes 38 and 39 of Fig. 1 from the tube 43. The signal which is to be switched from the output terminal 18 to the output terminal 19 is applied to the input terminal ||2 of the phase inverter tube 93.

It is believed that the mode of operation of the apparatus of Fig. 2 of the drawings will be obvious from the foregoing description of the operation of the apparatus of Fig. 1 of the drawings.

Fig. 3 of the drawings shows a system embodying the invention for alternating two inputs between two outputs. y

Referring to this figure of the drawings, reference numerals 6 and I8 indicate switching arrangements each of which are substantially identical with the apparatus shown by Fig. 2.

A phase inverter tube ||9 passes signals from the input terminal |2| into the switching arrangement ||6. The terminal |23 is available for applying signals to be switched by way of a phase inverter tube |24 to the switching arrangement ||8. Inasmuch as the arrangement of Fig. 3 so far described has been discussed in detail in connection with Fig. 2 of the drawings, a further detailed description of these parts will not be given.

An output connection comprising a source of anode supply voltage |26, mentioned later, and load resistor |29 is provided for an output tube |32. Resistor |28 together with condenser |31 constitute a decoupling filter to prevent reaction to and from tubes |32 and |39 and the power supply. A similar output connection comprising load resistor |36 is provided for the tube |38.

The tubes |32 and |38 correspond in function to the tubes 16 and 11 of Fig. 2 of the drawings. An output tube |39 has its output circuit also connected to the output resistor |29. Also, another output tube |4| is connected to the output resistor |36. The tubes |39 and |4| bear the same relationship to the arrangement H8 as the tubes |32 and |38 bear to the arrangement H6. Terminals |43 and |44 are the final output terminals at which signals from the input terminals 2| and |23 appear in accordance with the operation of the switching arrangements ||6 and ||8. The terminal |43 receives its signal from the cathode resistor |46 of an amplifier tube |41. The grid |48 of this tube is coupled to the output circuit of tubes |32 and |39 by a coupling' condenser |49 in conjunction with a grid resistor |5|.

The terminal |44 receives its signal from the cathode resistor |54 if an amplier tube |56, the grid |59 of which is connected by way of a coupling condenser |59 to the output circuit of the tubes |38 and |4I.

Switching signals or impulses are applied to the arrangements H6 and H8 over connections |62. Any desired source of switching signals may be employed, but the connections |62 are shown by way of example as being connected to a circuit |62 comprising a pair of discharge tubes |66 and |61 connected in the same manner as the tubes 44 and 45 of Fig. 1 of the drawings. Control signal potentials are applied to the grids of the tubes |66 and |81 by way of condensers |68 and |69. A convenient arrangement for applying control signals to these condensers is disclosed comprising a double-pole-double-throw switch |1. One set of stationary contacts |12 of this switch is connected to a pair of input terminals |13. If desired, a coded switching signal or two independent coded switching signals may be supplied to the terminals |13.

The other pair of stationary contacts |16 of the switch |1| is connected to a push-pull ampliiier |11 which serves to amplify input signals from a control signal source connected to terminals 18| or |82. A double-pole-double-throw switch |83 provides for connecting the amplifier |11 to either the terminals |8| or the termi nals |82.

The terminals |92 may be connected to a convenient source of alternating current of commercial frequency such as the source of heater current for any of the tubes shown. The terminals 18| may be connected to any other source of alternating current of any desired frequency. The' terminals |13, because of their direct connection to the grids of the tubes |66 and 81 without intervening transformers, are suitable for very low frequency or direct current switching signals.

Fig. l shows any well known power supply system or power pack |26, mentioned above, which may be employed to supply the various voltages required by the tubes in Fig. 3 of the drawings. The usual voltage divider with its filter condensers is shown diagrammatically and the taps on the voltagey divider labelled |86 to |88 are used to provide positive potentials to the tubes of Fig. 3. The connections from the tubes on Fig. 3 which are to be connected to these taps are labelled with corresponding numerals. Negative biasing potentials may be obtained from the tap 9|, and tube connections labelled |9| on Fig. 3 may be connected to this tap.

The operation of the switching arrangement shown in Fig. 3 of the drawings will be obvious from the fore-going discussion of the arrangement shown in Fig. 2. Briefly, an incoming signal applied to terminal |21 may follow a path through the tubes |96 and |91 so to appear in the output circuit of the tube I 32 which will result in the signal being switched to the nal output terminal |43 with tubes |96 and |91 conducting tubes |98 and |99 will be cut off. When the tubes |96 and |91 are cut off, the tubes |98 and |99 will be conducting so that the signal will appear in the output of the tube |38 and also in the signal output terminal |44. When the tubes |96 and |91 ar-e conducting, tubes 29| and 262 will also be conducting. When these last-named tubes are conducting, ytubes 203 and 204 will be cut off.

Signals applied simultaneously to the input terminals 12E and 23 will appear in the terminals M3 and E44 respectively, and after the reversal of operation of the tubes iii-i5 and itl, the signal from the terminal lill will appear in the final output terminal 44 and the input signal applied to the terminal E23 will appear in the final output terminal I 43.

Although only three arrangements employing a switch of the present invention are shown by way of illustration and example, it is possible, by suitable interconnection of the switches and switching voltages, to switch u inputs among the m output circuits.

The several switching arrangements disclosed herein are of general application and are specially suited to the operation of facsimile privacy systems such, for example, as is disclosed in the copending application of l-liallborg et al., Serial No. 491,537, iiled June 19, 1943, now Patent No. 2,425,616.

Having now described the invention, what is claimed and desired to be secured by Letters Patent is the following:

l. In an electronic switching system, a switching ampliiier comprising a or space discharge devices connected in push-pull relationship, each space discharge device comprising a cathode, an anode, and a control electrode, a control 'tube for said amplifier comprising a cathode, an anode, and a control electrode, nie-ans to supply a switching signal to said control electrode ci said control tube to cause said control tube to become conducting, means to supply positive operating voltage to said control tube, s, connection from said anode of said control tube to said anodes oi' said switching amplifier, and means to supply a voltage to said cathodes of said switching ainpliiier having a positive value at least equal to the voltage drop from cathode to anode of said control tube when it is conducting.

2. in an electronic switching system, a switching ampliiier comprising a pair of space' discharge devices connected in push-pull relationship, each space discharge device comprising a cathode, an anode, and a control electrode, a second switching amplifier comprising a pair ci space discharge devices connected in push-pull relationship, each space discharge device comprising a cathode, an anode, and a control electrode, a, pair of control tubes each having an anode, a cathode, and a control electrode, means to supply positive operating voltage to said anodes oi said control tubes, a capacitance interconnecting said control tube anodes, means to apply a switching signal selectively to said control electrodes oi control tub-es, a connection from said anode of one of said control tubes to said anodes oi said first-named switching anipliier tubes, and a connection from said anode of said second-named control tube to said anodes of said second-named switching arnpliler tubes.

3. An amplifying system comprising an arnplier, an output connection for said amplifier comprising a coupling device including a space dischage tube having a cathode, an anode, and a control electrode, an output circuit for said tube comprising a source oi anode voltage, a cathode circuit for said tube, a resistor in said cathode circuit, an impedance connecting said cathode to said amplifier, and a conductive connection from said ampliiier to said control electrode.

4. In an electronic switching system, a switching aniplier, an input circuit for said switching ampliiier, an output connection for said switching ainplier comprising a coupling device including a space discharge tube having a cathode, an anode, and a control electrode, an output circuit for said tube comprising a source of anode voltage, a cathode circuit for said tube, a resistor in said cathode circuit, an impedance connecting said cathode of said tube to said switching ampliier, and a conductive connection from said switching amplifier to said control electrode.

5. An electronic switching system comprising a plurality or" electronic switches, each electronic switch comprising a plurality o switching anipliiiers each having a cathode and an anode connection, a plurality of control tubes one for each oi said switching amplifiers in said electronic switches, each control tube having a cathode, an anode and a control electrode, means to supply a positive operating voltage to the anode of each of said control tubes, a connection from said operating voltage supply means for each contro-l tube anode to the anode connection of the switching amplifier associated with the control tube to supply a voltage depending on the condition of the associated control tube, an input connection for each or" said electronic switches, an output connection for each of the electronic switches, and means of such nature that said switches in operation under said control tubes function to alternate said input connections with said output connections.

J. ERNEST SlVilTH. EUGENE R. SHENK.

REFERENCES CITED The following references are of record in the ille oi this patent:

UNITED STATES PATENTS Number Name Date 2,055,883 Terry Sept. 29, 1936 2,089,430 Roy et al Aug. 10193'7 2,140,004 Falloon Dec. 13, 1938 2,146,862 Shuniard Feb. 14, 1939 2,189,317 Koch Feb. 6, 1940 2,221,115 Shepard, Jr Nov. 12, 1940 2,265,868 Schonland Dec. 9, 1941 2,272,099 Reeves Feb. 3, 1942 2,309,999 Williams Nov. 3, 1942 2,324,314 Michel July 13, 1943 FOREIGN PATENTS Number Country Date 356,111 Great Britain Aug. 24, 1931 

